1. Technical Field
This invention relates to a chain saw safety switch that is grasped and held by a human operator during the normal operation of such chain saw and, while so grasped and held, automatically rotates when "kick-back" occurs to independently actuate such chain saw's on-off switch that controls the engine driving the cutting chain to stop such cutting chain.
2. Background Art
The prior art, U.S. Pat. No. 3,664,390, discloses safety means for power-driven chain saws; U.S. Pat. No. 3,776,331 discloses a brake-device for power saws; U.S. Pat. No. 3,934,345 discloses a snap-acting over-center chain saw safety brake and method of operation thereof; U.S. Pat. No. 3,964,333 discloses a safety braking mechanism for a portable chain saw; U.S. Pat. No. 3,991,469 discloses a safety braking mechanism for a portable chain saw; U.S. Pat. No. 3,991,864 discloses a motor saw, especially motor chain saw; U.S. Pat. No. 3,992,779 discloses a chain brake for chain saw; U.S. Pat. No. 4,026,392 discloses a snap-acting over-center chain saw safety brake and method of operation thereof; U.S. Pat. No. 4,121,339 discloses a safety brake mechanism for chain saws; U.S. Pat. No. 4,156,477 discloses a braking system of chain saw; U.S. Pat. No. 4,324,045 discloses a motor chain saw with dynamic safety braking device; U.S. Pat. No. 4,334,357 discloses a safety braking apparatus for a portable chain saw.
The following discussion focuses on the problems inherent in the prior art and how this invention contributes to the solution of such prior-art problems.
"Kick-back" means that the outgoing run of the cutting chain is jammed, caught or otherwise encounters resistance thereby causing the cutter bar mounting such cutting chain to be thrown back towards the human operator's face, neck or chest with consequent serious injury or even death. For example, a right-handed human operator grasps and holds the chain saw with his left hand holding a cross-wise, gripping front handle and his right hand holding a rear control handle aligned with the front to rear longitudinal axis of such chain saw. When "kick-back" occurs, the human operator's left hand, holding such cross-wise front handle, rotates or moves forward on such front handle. The object of this invention is to utilize this physical fact of the movement of the human operator's hand holding such front handle when "kick-back" occurs to shut off the engine and stop the cutting chain.
The object of this invention is to contribute to the solution of such prior-art problems by providing an elongated safety handle of open-cylindrical configuration that is rotatively mounted by the existing front handle. The safety handle is operatively connected to the existing on-off switch to shut off the engine and stop the cutting chain when kick-back occurs. The safety handle has an "on" position and and "off" position. The safety handle must be rotated to its "on" position and the existing on-off switch must be switched on before the chain saw can be started. The human operator grasps and holds the safety handle during normal operation and running of the chain saw and he can shut off the engine and stop the cutting chain by simply rotating the safety handle forward in a clockwise direction. When kick-back occurs, the cutter bar will be thrown back toward the human operator; and, since such kick-back occurs while he is still grasping and holding the safety handle, the safety handle will automatically be rotated forward in a clockwise direction to independently actuate the on-off switch to shut off the engine and stop the cutting chain.
The safety handle of this invention requires the human operator to place his chain saw on the ground before starting same. If he attempts to start his chain saw while holding same off the ground, the torquing engine will cause the cutter bar to rotate counterclockwise and the human operator's hand grasping the safety handle will again automatically rotate the safety handle clockwise shutting off the engine and stopping the cutting chain.
During severe kick-back or throw, or when the chain saw is dropped, the human operator's hand will not be grasping and holding the safety handle but instead his hand will strike a wrist guide operatively connected with the safety handle to cause it to rotate clockwise to shut off the engine.
This invention also features an automatic reset mechanism for the handle. The safety handle is biased by a compression spring to its "on" position. Rotation of such safety handle to its "off" position imposes a compressive bias upon such spring whose restoring force, upon relief from such compressive bias, automatically rotates and restores the safety handle to its "on" position.